This application claims the benefit of Korean Patent Application No. 2002-10657, filed on Feb. 27, 2002 in Korea, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a transflective liquid crystal display (LCD) device and a method of manufacturing the same.
2. Discussion of the Related Art
In general, the liquid crystal display (LCD) device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode and the electrodes of each substrate are also facing each other. Voltage is applied to each electrode and an electric field is induced between the electrodes. An alignment of the liquid crystal molecules is changed by varying the intensity of the electric field. The LCD device displays a picture by varying transmittance of the light according to the arrangement of the liquid crystal molecules.
Because the liquid crystal display (LCD) device is not luminescent, it needs an additional light source in order to display images. The liquid crystal display device is categorized into a transmissive type and a reflective type depending on the type of light source.
In the transmissive type, a backlight is used as a light source behind a liquid crystal panel. Light incident from the backlight penetrates the liquid crystal panel, and the amount of the transmitted light is controlled depending on the alignment of the liquid crystal molecules. Here, the substrates are usually transparent and the electrodes of each substrate are usually formed of transparent conductive material. As the transmissive liquid crystal display (LCD) device uses the backlight as a light source, it can display a bright image in dark surroundings. Because an amount of the transmitted light is very small for the light incident from the backlight, the brightness of the backlight must be increased in order to increase the brightness of the LCD device. Consequently, the transmissive liquid crystal display (LCD) device has high power consumption due to the operation of the backlight.
On the other hand, in the reflective type LCD device, sunlight or artificial light is used as a light source of the LCD device. The light incident from the outside is reflected at a reflective plate of the LCD device according to the arrangement of the liquid crystal molecules. Since there is no backlight, the reflective type LCD device has much lower power consumption than the transmissive type LCD device. However, the reflective type LCD device cannot be used in dark surroundings because it depends on an external light source.
Therefore, a transflective LCD device, which can be used both in a transmissive mode and in a reflective mode, has been recently proposed. A conventional transflective LCD device will be described hereinafter more in detail.
FIG. 1 is an exploded perspective view illustrating a conventional transflective LCD device. The conventional transflective LCD device 11 has upper and lower substrates 15 and 21, which are spaced apart from and facing each other, and also has a liquid crystal layer 14 interposed between the upper substrate 15 and the lower substrate 21.
A gate line 25 and a data line 39 are formed on the inner surface of the lower substrate 21. The gate line 25 and the data line 39 cross each other to define a pixel area xe2x80x9cPxe2x80x9d. The pixel area xe2x80x9cPxe2x80x9d includes a transmissive region xe2x80x9cBxe2x80x9d and a reflective region xe2x80x9cAxe2x80x9d. A thin film transistor xe2x80x9cTxe2x80x9d is situated at the crossing of the gate line 25 and the data line 39. A reflective electrode 49 having a transmissive hole 49a and a transparent electrode 61 overlapping the reflective electrode 49 are formed in the pixel area xe2x80x9cPxe2x80x9d. The reflective electrode 49 and/or the transparent electrode 61 are connected to the thin film transistor xe2x80x9cTxe2x80x9d. The transmissive hole 49a corresponds to the transmissive region xe2x80x9cBxe2x80x9d.
Meanwhile, a black matrix 16, which has an opening corresponding to the reflective electrode 49 and the transparent electrode 61, is formed on the inside of the upper substrate 15, and a color filter 17 corresponding to the opening of the black matrix 16 is formed on the black matrix 16. The color filter 17 is composed of three colors: red (R), green (G) and blue (B). Each color corresponds to each pixel area xe2x80x9cPxe2x80x9d. Subsequently, a common electrode 13 is formed on the color filter 17.
FIG. 2 is a schematic cross-sectional view of a conventional transflective LCD device. FIG. 2 indicates a pixel area of the conventional transflective LCD device. In the conventional transflective LCD device 11, a reflective electrode 49 is formed on the inner surface of a lower substrate 21 and an insulating layer 50 is formed on the reflective electrode 49. The reflective electrode 49 has a transmissive hole 49a corresponding to a transmissive region xe2x80x9cBxe2x80x9d. A transparent electrode 61 is formed on the insulating layer 50. As stated above, the lower substrate 21 includes a gate line (not shown), a data line (not shown) and a transistor (not shown) thereon.
An upper substrate 15 is spaced apart from and facing the lower substrate 21. A common electrode 13 is formed on the inner surface of the upper substrate 15. Though not shown in the figure, a black matrix and a color filter are subsequently formed between the upper substrate 15 and the common electrode 13.
A liquid crystal layer 14 is disposed between the lower and upper substrates 21 and 15, and molecules of the liquid crystal layer 14 are arranged horizontally with respect to the substrates 21 and 15.
Polarizers (not shown) are arranged on the outer surface of the lower and upper substrate 21 and 15. The transmission axes of polarizers are perpendicular to each other.
A backlight 41 is located under the outside of the lower substrate 21. The backlight 41 is used as a light source of a transmissive mode of the transflective LCD device.
In a transmissive mode, the first light xe2x80x9cF1xe2x80x9d from the back light 41 penetrates the transparent electrode 61 in the transmissive region xe2x80x9cBxe2x80x9d. Next, while the first light xe2x80x9cF1xe2x80x9d passes through the liquid crystal layer 14, the amount of the first light xe2x80x9cF1xe2x80x9d is controlled by the arrangement of the liquid crystal layer depending on applied voltage. Then the first light xe2x80x9cF1xe2x80x9d is emitted.
On the other hand, in a reflective mode, the second light xe2x80x9cF2xe2x80x9d incident from the outside such as sunlight or artificial light passes through the liquid crystal layer 14 and is reflected at the reflective electrode 49 in a reflective region xe2x80x9cAxe2x80x9d. The second light xe2x80x9cF2xe2x80x9d goes through the liquid crystal layer 14 again and is emitted. At this time, the amount of emitted second light xe2x80x9cF2xe2x80x9d is controlled according the arrangement of liquid crystal molecules.
Because of different optical paths of the first and second lights xe2x80x9cF1xe2x80x9d and xe2x80x9cF2xe2x80x9d, the polarizing properties of the emitted lights are different from each other. That is, the first light xe2x80x9cF1xe2x80x9d passes through the liquid crystal layer only once while the second light xe2x80x9cF2xe2x80x9d passes through the liquid crystal layer twice. Therefore, the transmittance is different in the transmissive mode and in the reflective mode as the cell gap is uniform, and it is difficult to realize high definition.
Recently, transflective LCD devices that simultaneously optimize the transmittance of a transmissive mode with the brightness of a reflective mode have been proposed. These transflective LCD devices are described with reference to the attached figures.
FIG. 3 is a plan view showing an array substrate for a transflective liquid crystal display (LCD) device according to a first embodiment of the related art. In FIG. 3, a gate line 25 is formed horizontally in the context of the figure and a data line 39 is formed vertically in the context of the figure. The gate and data lines 25 and 39 cross each other to define a pixel region xe2x80x9cPxe2x80x9d, which includes a transmissive region xe2x80x9cBxe2x80x9d and a reflective region xe2x80x9cAxe2x80x9d. At the crossing of the gate and data lines 25 and 39, a thin film transistor xe2x80x9cTxe2x80x9d is formed and the thin film transistor xe2x80x9cTxe2x80x9d is electrically connected to the gate and data lines 25 and 39. A transparent electrode 61 and a reflector 49 are formed in the pixel region xe2x80x9cPxe2x80x9d. The transparent electrode 61 is a pixel electrode of the array substrate and is connected to the thin film transistor xe2x80x9cTxe2x80x9d. The reflector 49 may be a reflective electrode when the reflector 49 is electrically connected to the thin film transistor xe2x80x9cTxe2x80x9d. Meanwhile, a first passivation layer (not shown) is formed under the reflector 49 and the first passivation layer has a first transmissive hole 27 corresponding to the transmissive region xe2x80x9cBxe2x80x9d. The first transmissive hole 27 is to optimize the transmittance of a transmissive mode with the transmittance or optical efficiency of a reflective mode. An inclined portion 27a surrounds the first transmissive hole 27 and is covered with the reflector 49. The reflector 49 also has a second transmissive hole 49a corresponding to the first transmissive hole 27.
An arrow xe2x80x9cG1xe2x80x9d shows an alignment direction of an alignment layer (not shown) to be formed on the top of the array substrate.
FIG. 4 is a cross-sectional view along the line IVxe2x80x94IV of FIG. 3. In FIG. 4, a gate insulator 22 and a first passivation layer 23 subsequently are formed on a substrate 21. A reflector 49 is formed on the first passivation layer 23. The first passivation layer 23 has a first transmissive hole 27 corresponding to a transmissive region xe2x80x9cBxe2x80x9d and also the reflector 49 has a second transmissive hole 49a. An inclined portion 27a is formed around the first transmissive hole 27.
A second passivation layer 28 is formed on the reflector 49 and a transparent electrode 61 is formed on the second passivation layer 28. An alignment layer 63 is formed on the transparent electrode 61 and the surface of the alignment layer 63 is arranged in a direction of the arrow xe2x80x9cG1xe2x80x9d of FIG. 3 by a rubbing method. Though not shown in the figure, a thin film transistor is formed on the substrate 21.
Since the first transmissive hole 27 makes a liquid crystal layer (not shown) of the transmissive region xe2x80x9cBxe2x80x9d about two times the thickness of that of the reflective region xe2x80x9cAxe2x80x9d, the optical characteristic of the transmissive mode is optimized with the optical characteristic of the reflective mode.
However, as stated above, the inclined portion 27a is formed between the transmissive region xe2x80x9cBxe2x80x9d and the reflective region xe2x80x9cAxe2x80x9d, and the thickness of the liquid crystal layer (not shown) disposed on the inclined portion 27a changes continuously. Accordingly, when the voltage is applied to the transflective LCD device, a fringe field is produced in the inclined portion 27a and a distortion occurs. Also, the phase difference of the liquid crystal layer varies in the region, and thus light leakage occurs. Therefore, the reflector 49 covers the inclined portion 27a in order to prevent light leakage.
However, when the alignment direction xe2x80x9cG1xe2x80x9d is about xe2x88x9245 degrees with respect to the gate line 25 of FIG. 3, the arrangement of the alignment layer is poor in a neighboring region xe2x80x9cIxe2x80x9d of the inclined portion 27a. Accordingly, light leakage occurs in the region xe2x80x9cIxe2x80x9d in the transmissive mode. The light leakage is shown in FIG. 5.
As shown in FIG. 5, the light leakage 50 occurs in the upper and left sides in the context of the figure (circled) of the transmissive region xe2x80x9cBxe2x80x9d of FIGS. 3 and 4, wherein the upper and left sides correspond to the neighboring region xe2x80x9cIxe2x80x9d of the inclined portion 27a of FIG. 4. During rubbing, the rubbing cloth may not reach the areas in region xe2x80x9cIxe2x80x9d due the xe2x88x9245xc2x0 alignment direction shown in FIG. 3 and the arrangement of the alignment layer 63 of FIG. 4 is poor in the region xe2x80x9cIxe2x80x9d. The light leakage 50 fairly lowers the contrast ratio of the transflective LCD device.
On the other hand, another structure of an. array substrate for the transflective LCD device to block the light leakage is suggested in FIGS. 6 and 7. FIG. 6 is a plan view of showing an array substrate for a transflective liquid crystal display (LCD) device according to a second embodiment of the related art and FIG. 7 is a cross-sectional view along the line VIIxe2x80x94VII of FIG. 6. Here, FIG. 6 shows only the pixel region xe2x80x9cP,xe2x80x9d and the array substrate has the same structure as that of the related art first embodiment except for the reflector. The alignment direction of the array substrate of FIG. 6 is about xe2x88x9245 degrees with respect to a gate line (not shown), which is horizontal in the context of the figure.
In FIGS. 6 and 7, the reflector 49 extends into the inside of the transmissive region xe2x80x9cBxe2x80x9d, covering the inclined portion 27a. Therefore, the light leakage in the region xe2x80x9cIxe2x80x9d is blocked.
As the region xe2x80x9cIxe2x80x9d does not belong to either the transmissive mode or the reflective mode, the aperture ratio decreases. Since a pixel pitch is very small in an LCD device having a high resolution, the aperture ratio is reduced.
Accordingly, the present invention is directed to an array substrate for a transflective liquid crystal display (LCD) device and a method of manufacturing the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an array substrate for a transflective liquid crystal display (LCD) device that has high aperture ratio and high resolution and in which no light leakage occurs.
Another advantage of the present invention is to provide a method of manufacturing an array substrate for a transflective liquid crystal display (LCD) device that has high aperture ratio and high resolution and in which no light leakage occurs.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a transflective liquid crystal display device includes a first substrate; a gate line and a data line on the first substrate, wherein the gate and data lines cross each other to define a pixel region having a transmissive region and a reflective region; a thin film transistor electrically connected to the gate and data lines; a first passivation layer covering the thin film transistor, wherein the first passivation layer has a first transmissive hole corresponding to the transmissive region and an inclined portion surrounding the first transmissive hole; a reflector on the first passivation layer covering sides of the transmissive region asymmetrically, wherein the reflector corresponds to the reflective region; a second passivation layer on the reflector; and a transparent electrode on the second passivation layer, wherein the transparent electrode electrically contacts the thin film transistor. The asymmetric location of the reflector on the sides of the transmissive region is determined by the alignment direction.
The transflective liquid crystal display device further includes a black matrix on a second substrate spaced apart over the array substrate. The black matrix overlaps the data line and covers at least a side of the inclined portion.
In another aspect, a method of manufacturing a transflective liquid crystal display device includes forming a gate line on a first substrate; forming a data line crossing the gate line, the data line and the gate line defining a pixel region, the pixel region having a transmissive region and a reflective region; forming a thin film transistor electrically connected to the gate and the data lines; forming a first passivation layer on the thin film transistor, wherein the first passivation layer has a first transmissive hole corresponding to the transmissive region and an inclined portion surrounding the first transmissive hole; forming a reflector corresponding to the reflective region on the first passivation layer covering sides of the transmissive region asymmetrically; forming a second passivation layer on the reflector; and forming a transparent electrode electrically contacting the thin film transistor on the second passivation layer. The asymmetric location of the reflector on the sides of the transmissive region is determined by the alignment direction.
The method of manufacturing the transflective liquid crystal display device further includes forming a black matrix on a second substrate spaced apart over the first substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.